<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      let score = +prompt('输入您的分数')
      if (score >= 90) {
        alert('A')
      } else if (score < 90 && score >= 80) {
        alert('B')
      } else if (score < 80 && score >= 70) {
        alert('C')
      } else if (score < 70 && score >= 60) {
        alert('D')
      } else if (score < 60) {
        alert('E')
      }
    </script>
  </body>
</html>
